Microelectronic packaging for high power semiconductor devices must increase the thermal conductivity of its integrated heat spreader for improved thermal dissipation of heat produced by high power semiconductor devices housed within the microelectronic packaging and seated on the heat spreader.
Microelectronic packaging (referred to herein as “a package”) typically includes a stacked configuration of a heat spreader, a substrate material (i.e. an electrical insulator) that is high-temperature-brazed to the heat spreader, and leads that are high-temperature-brazed to the heat spreader. A thermal expansion mismatch between the electrical insulator and the heat spreader manifests as excessive package deflection. Excessive package deflection (i.e., camber) contributes to high bending (i.e., flexural) mechanical stress in the insulator which may cause fractures of the insulator. More specifically, during cooling of the brazed assembly, the thermal expansion difference between the heat spreader and the insulator may cause excessive deflection of the package which results in the package being more vulnerable to brittle fractures.
In addition, excess package deflection decreases the surface area of the package that is in contact with a second level assembly. Therefore, thermal pathways extending from the high power semiconductor devices, through the heat spreader and into the second level assembly are reduced and/or are not direct. As such, the heat dissipation of the package decreases, and the effectiveness of the heat spreader is reduced.
A variety of efforts have been made to address the large differential between the Coefficient of Thermal Expansion (CTE) of the heat spreader and the CTE of the insulator to decrease deflection. For example, CPC (copper-moly/copper-copper) laminate heat spreaders are cost effective, and provide a good thermal expansion and a better match to the CTE of the insulator. However, these heat spreaders have proven to be too low in thermal conductivity which inhibits thermal energy transfer.